In-office carotid ultrasound helps estimate risk.
Increased carotid intimal-medial thickness (IMT) constitutes a reliable surrogate marker for coronary artery disease (CAD). The information gleaned through such testing often substantially alters an individual's cardiovascular risk status, changing the aggressiveness of primary preventive therapy, said Dr. Douglas, the Tuchman Professor of Medicine and head of cardiovascular medicine at the University of Wisconsin, Madison.
She and her Madison colleagues have developed a vascular health screening program in which carotid IMT measurement plays a central role.
The underlying concept is that the biologic age of a patient's arteries--their wear and tear as reflected in plaque burden measured as carotid IMT--is more important to coronary and cerebrovascular risk than the arteries' chronologic age. By substituting vascular age for chronologic age in the standard Framingham 10-year risk score calculation, Dr. Douglas explained, one obtains a truer estimate of an asymptomatic individual's risk.
The relationship between the carotid artery and the coronaries is the same as that between one coronary artery and another. The same risk factors for atherosclerotic disease apply to both.
Landmark prospective studies including the Cardiovascular Health Study and the Atherosclerosis Risk In Communities (ARIC) study have shown that carotid IMT accurately predicts cardiac and cerebrovascular events. Indeed, carotid IMT is the only surrogate end point for CAD accepted as valid by the Food and Drug Administration for use in clinical trials of lipid-lowering and antihypertensive drugs, noted Dr. Douglas, who is ACC vice president.
In developing their novel vascular health screening program, the Wisconsin cardiologists created a linear regression model based upon published ARIC study nomograms for IMT in a normal population. This enabled physicians to determine a patient's vascular age.
Of the first 78 patients to go through the vascular health screening program, IMT measurement showed that 71% had arteries that were older than expected based upon their chronologic age. "Forty percent of patients had arteries that were 10 years or more older" than their chronologic age, Dr. Douglas said.
By substituting vascular age for chronologic age, the study population's mean Framingham risk score climbed from 6.5 to 8.
Cardiovascular risk increased in 46% of patients and was revised downward in 20%. A greater than 5% shift in Framingham risk score occurred in nearly one-third of patients. Overall, 15% of patients received more aggressive preventive pharmacotherapy as a result; 4% were shifted to less aggressive therapy.
The greatest impact of incorporating carotid IMT into the risk assessment was seen in patients classified as intermediate risk using the conventional Framingham scoring as recommended in National Cholesterol Education Program guidelines.
Of these patients, 50% were reclassified after carotid IMT was incorporated into the risk calculation; in most of these cases, the patients were bumped up into a higher-risk category.
Carotid IMT, measured using conventional ultrasound equipment, is relatively inexpensive to perform. But there's a caveat: The measurements involved are small, and painstaking standardized methods are required to achieve good reliability. Dr. Douglas and her colleagues used the IMT imaging protocol laid out by ARIC investigators.
BY BRUCE JANCIN
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|Title Annotation:||IMT Reliable Surrogate Marker|
|Publication:||Internal Medicine News|
|Date:||Mar 15, 2004|
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